Digester



M y 28, 1940. A. c. DURE JIN, JR 2,202,772

I DIGESTER Filed NOV. 29, 1937 Patented May 28, 1940 UNITED STATES PATENT OFFICE DIGESTER Augustus C. Durdin, Jr., Chicago, Ill., assignor to Chicago Pump Company, Chicago, 11]., a corporation of Illinois Application November 29, 1937, Serial No. 177,082

wall I 8 and a vertical wall l9 depending there- 8 Claims.

This invention relates to digesters and particularly to digesters in which the decomposition of sewage, sludge, and other organic materials is conducted under anaerobic conditions.

Organic decomposition of this type is accompanied by the evolution of gas of considerable calorific value. This gas is normally burned for useful purposes and usually at least some of the heat derived therefrom is utilized for the heating of thematei'ial being decomposed, since the decomposition is considerably accelerated by reasonably high temperature, of the order of 90 or 100 F.

In digestion as heretofore practiced, considerable difliculty has been experienced by the formation of a solid cake or crust within the digester, particularly in the zone of the liquid level. It is believed that the gas produced in the process carries solidmaterials upwardly and causes them to float and these floating solid materials for some reason or other tend to agglomerate at the surface of the liquid and to coalesce on the apparatus at that level.

One of the principal objects of the invention is to provide apparatus in which the formation of a crust in excessive amounts is prevented.

A further object of the invention is to provide improved means for storing a certain amount of gas in the digester and for utilizing said storage means for maintaining the solids submerged against any tendency to float.

The invention willreadily be understood from the following description of a preferred embodiment thereof, taken' in conjunction with the accompanying drawing which is a vertical sectional view through a digester embodylngmy invention.

The digester comprises a basin H) which may suitably be built of concrete. This basin may be round, square, or of other suitable shape in crosssectlon. It is preferably relatively deep and is provided with a hopper bottom ll. At its lowermost point the tank is provided'with an outlet pipe I2 controlled by a valve l3, so that the mud-like precipitate resulting from the decomposition may be drawn ofi at will.

Within the tank I is a heating coil l4 through which circulates any suitable medium heated by the combustion of some or all of the gas produced by the digester. in well-known manner. The tank Ill is provided with an inlet l5 which is provided with a valve l6, whereby the admission of sludge, sewage, or other materials which are to be decomposed, maybe controlled. A

gas-holding bell I! is located in the upper part of the tank Hi. This bell may have a fiat upper the shape of the tank Ill. The wall [9 is somewhat smaller than the interior outline of the tank l0 so that the bell I1 may movefreely within the tank.

An impervious conduit or pipe 20 extends from a position a short distance below the upper wall of the gas bell I1 and extends downwardly in a vertical direction to a point somewhat above the lower edge of the gas bell. The pipe 20 is supported from the upper wall IBof the gas bell I! by means of brackets 2i. tance above the lower end of the pipe 20 I provide a horizontal perforate wall .22 which extends from the pipe 20 to the skirt or vertical wall I9 of the bell ll. This perforate wall is mounted in position by being secured to the pipe 20 and the vertical wall Hi. It may suitably consist of .a woven screen of suitable mesh to prevent any but the smallest solids from passing through. Thus, I may employ a wire screen of A" mesh or finer screen, such as or {3" mesh, or a screen of even finer mesh. In some cases, however, I prefer to employ a grille or screen having a larger opening size or mesh.

A gas outlet pipe 23 extends into a tank I and terminates in an upwardly directed vertical length 24 which projects freely through the pipe 20 to a point above the normal surface level of the liquid which is defined by an overflow pipe 25 which extends from an intermediate position on the tank III at a place remote from the inlet I5. The overflow pipe 25 extends upwardly to a lead-01f pipe 26 located at the desired liquid level of the tank. I Stops 21, suitably projecting from the wall of the tank to, prevent excessive movement of the bell ll into the'tank IIL,

The operation is as follows: The material to be digested is'introduced by the inlet l5 so as to fill the tank up to the level defined by the outlet pipe 25, 26. The valve controlling the pipe 23 is opened so as to allow substantially all the air in the bell I! to escape and to allow the liquid to enter into the bell to the liquid level, through the perforated partition 22. It is to be noted that the perforated partition 22 prevents solid material from rising into the upper part of the bell and these solid materials are therefore maintained submerged at all times. Heated medium is passed through the coil l4 and the liquid is brought to a suitable digesting temperature.

The decomposing material produces gas which rises upwardly through the screen 22 and collects in the bell l1. Some of this gas forms in solid from, which wall closely conforms in shape to At a level a short dismaterials and floats them into contact with the perforated wall 22. Owing to the foraminous nature of the wall 22, the gas is allowed to free itself from the solid materials andpass upwardly into the upper part of .the bell l1. When solid materials are freed from gas in this way, they sink downwardly and tend to disintegrate. As the gas accumulates in the bell H, the bell rises and in normal operation the gas is drawn oil by the pipe 23 at sufiicient rate to maintain the bell I! at an intermediate position floating on the liquid in the tank Ill.

The varying positions of the bell l1 relative to the level of the liquid causes flow of the liquid in both directions through the perforated wall or screen 22 and this current efiectively cleans the wall or screen 22 and prevents it from becoming I choked.

, In the event that the perforated wall or screen 22 does become 'choked to some extent, the gas produced will accumulate beneath this wall owing to the projection of the tube 20 below the wall, and consequently the liquid above the wall will flow down through partially choked openings in the wall 22 and will remove material from these openings. In any event, the hell I! floating freely on the liquid in the tank In and being unsecured in any way, it may readily be removed, the screen or wall 22 cleaned, whereupon the bell may be reinstalled.

Although the invention has been disclosed in connection with the specific details of a preferred embodiment thereof, it must be understood that such details are not intended to be'limitative of the invention except in so far as accompanying claims.

Having thus described my invention, what I claim'as new and desire to secure by Letters Patent of the United States is:

1. A digester comprising a basin, gas bell adapted to float in the upper part of said basin, and a foraminous wall mounted on, and

extending across said bell adapted normally to be submerged in the liquid therein,

being adapted to maintain normal sludge solids said wall submerged.

2. A digester comprising a basin, an inverted gas bell adapted to float in said basin, and a foraminous wall carried by and extending across the interior of the lower portion of said bell, said wall being adapted to maintain normal sludge solids submerged.

3. A digester comprising a basin, an inverted gas bell adapted to float in said basin, a conduit within the bell extending from the lower portion of the bell to a point slightly below the upper end set forth in the an inverted resting solid materials submerged, maintaining of the bell, and a foraminous wall mounted on the bell within the lower part of the bell and extending between said bell and said conduit, said wall being adapted to maintain normal sludge solids submerged.

4. A digester comprising a basin, aninverted gas b'ell adapted to float in said basin, a conduit within the bell extending from a point above the lower edge of the bell to a point slightly below the upper end of the bell, and a foraminous wall mounted on the bell within the lower part of the bell and extending between said bell and. the conduit at a position above the lower end of said conduit, said wall being adapted to maintain normal sludge "solids submerged.

5. In a digester, in combination, a basin,'a foraminous wall therein adapted to be submerged in normal operation, means below said wall for introducing liquid to be digested, means above said wall for collecting gases produced in saidbasin, mal sludge solids submerged, and means actuated by said gases for varying-the position of said foraminous wall in the basin.

6. The method of digesting liquid containing organic materials which consists in maintaining a body of liquid under digesting and gas forming conditions, arresting solid materials tending to float owing to gas adherence-and maintaining them submerged by a submerged screen while maintaining free degasing conditions to enable the solid material to be degased and caused to sink, maintaining said screen ubmerged in the liquid, and varying the level of said screen whereby liquid fiows therethrough.

. '7. In a method of digesting, in combination, maintaining liquid containing organic materials under digesting and e v resting solid materials and maintaining them submerged by a submerged screen, maintaining free passage for gas above said solid materials whereby gas may separate therefrom and move submerged in displacing liqupwardly, maintaining said screen the liquid, collecting said gas, and uid through said screen by said gas. J 8. In a method of digesting, in combination, maintaining liquid containing organic materials under digesting and gas forming conditions, ar-

free passage for gas above said solid materials whereby gas may separate'therefrom and move upwardly, causing liqgas forming conditions, ar-

and maintaining them uid to flow past said submerged solidmaterials in Y both directions, and moving said arrested solid materials to various levels in the liquid.

. AUGUS'I'IIS C. DURDIN, JR. 

